Common Antibiotic Dosage ð
Irish educational reference for common adult antibiotic doses by route, with Irish brand names, key warnings, and SmPC links. Search by drug or brand. Confirm local antimicrobial guidelines before prescribing.
Adult antibiotic doses
Search by drug or Irish brand name. Usual SmPC doses for normal organ function.
Educational use only
- Confirm the current Irish SmPC, local AMS protocol, allergy status, and organ function before prescribing.
- Doses are usual adult regimens. Indication and severity can change the dose.
- Gentamicin and vancomycin: follow local TDM / AMS nomograms as well as the SmPC.
35 dose rows. Type to filter.
| Drug | Route | Usual adult dose | Frequency | Key warnings |
|---|---|---|---|---|
| Penicillins | ||||
| Amoxicillin (Amoxil) | PO | 250â500 mg (CAP: 500 mgâ1 g) | Every 8 h | SmPC is indication-based. Severe sinusitis/otitis may use 750 mgâ1 g every 8 h. GI upset; C. difficile risk. |
| Amoxicillin | IV | 500 mgâ1 g | Every 8 h | Use the IV product SmPC. Higher doses exist for severe infection. Confirm local stock / AMS. |
| Co-amoxiclav (Augmentin) | PO | 500/125 mg (625 mg tablet) | TDS | SmPC usual adult dose: one 500/125 mg three times a day. Take with food. Cholestatic jaundice risk with prolonged courses. |
| Co-amoxiclav (Augmentin) | PO | 875/125 mg | BD (TDS = higher dose) | SmPC: BD for all indications; TDS for higher-dose needs (e.g. otitis, sinusitis, LRTI, UTI). Take with food. |
| Co-amoxiclav (Augmentin) | IV | 1.2 g (1000/200 mg) | Every 8 h | Usual adult IV SmPC dose. Review daily and switch to PO when suitable. |
| Flucloxacillin (Floxapen) | PO | 250â500 mg | QDS (or TDS) | Irish Floxapen SmPC: usual total 1â3 g/day in 3â4 divided doses (often 250â500 mg QDS). Empty stomach. Hepatotoxicity risk. |
| Flucloxacillin (Floxapen) | IV | 250 mgâ1 g (may be doubled if severe) | QDS | Usual IV SmPC range 250 mgâ1 g QDS; may be doubled in severe infection. Osteomyelitis/endocarditis: higher totals per product SmPC / AMS. |
| Phenoxymethylpenicillin (Pen V) | PO | 250â500 mg | QDS | Empty stomach preferred. Not for serious systemic infection. |
| Benzylpenicillin (Crystapen) | IV / IM | 600 mgâ1.2 g | Every 6 h | SmPC usual adult range; q4â6 h and higher totals for severe infection per product SmPC. Sodium load. |
| Piperacillin-tazobactam (Tazocin) | IV | 4.5 g (4 g/0.5 g) | Every 8 h (every 6 h if severe pneumonia / FN) | See dedicated Tazocin topic / SmPC. No reliable oral switch. Pseudomonas cover. |
| Cephalosporins | ||||
| Cefuroxime (Zinnat) | PO | 250 mg (500 mg if severe / LRTI) | BD | After food. Not a like-for-like oral switch from IV cefuroxime. |
| Cefuroxime (Zinacef / Flynn) | IV | 750 mg (1.5 g if severe) | TDS | SmPC usual 750 mg TDS; 1.5 g TDS for more serious infections. Confirm local AMS. |
| Ceftriaxone (Rocephin) | IV / IM | 1â2 g | OD | SmPC usual adult range. Do not mix with calcium-containing infusions. Meningitis: higher dose per SmPC / protocol. |
| Cefalexin (Keflex) | PO | 500 mg (alt. 250â500 mg) | Every 8 h (alt. every 6â12 h) | SmPC: most infections 500 mg every 8 h; SSTI/pharyngitis/mild UTI often 250 mg every 6 h or 500 mg every 12 h. Usual total 1â4 g/day. |
| Macrolides & tetracyclines | ||||
| Clarithromycin (Klacid) | PO | 250 mg (500 mg if severe) | BD | SmPC: usual 250 mg BD; increase to 500 mg BD in severe infection. CYP3A4 interactions; QT prolongation. |
| Clarithromycin (Klacid IV) | IV | 500 mg | BD | Same interaction / QT cautions as PO. Switch to PO when absorbing. |
| Azithromycin (Zithromax) | PO | 500 mg | OD for 3 days | SmPC respiratory regimen commonly 500 mg once daily for 3 days (or day-1 500 mg then 250 mg for 4 days: check SmPC indication). QT risk. |
| Doxycycline (Vibramycin) | PO | 200 mg day 1, then 100 mg | OD (or 100 mg BD) | SmPC usual: 200 mg on day 1, then 100 mg daily; 100 mg BD may be used. Avoid in pregnancy / children <12. Take upright with fluid. |
| Quinolones, metronidazole & clindamycin | ||||
| Ciprofloxacin (Ciproxin) | PO | 250â750 mg | BD | SmPC dose is indication-based within this range. Tendinopathy, CNS effects, QT, C. difficile. Separate from dairy/antacids. |
| Ciprofloxacin | IV | 400 mg | Every 12 h (every 8 h if severe) | SmPC usual 400 mg every 12 h; every 8 h for severe infection. Switch to PO when absorbing. |
| Metronidazole (Flagyl) | PO | 800 mg load, then 400 mg | Every 8 h | Irish Flagyl SmPC for established anaerobic infection: 800 mg then 400 mg every 8 h. Other indications differ (e.g. BV 400 mg BD). Avoid alcohol. |
| Metronidazole (Flagyl) | IV | 500 mg | Every 8 h | Usual adult IV anaerobic dose. Switch to PO early when possible. Avoid alcohol. |
| Clindamycin (Dalacin C) | PO | 150â300 mg (severe: 300â450 mg) | Every 6 h | SmPC: moderately severe 150â300 mg every 6 h; severe 300â450 mg every 6 h. High C. difficile risk. |
| Clindamycin (Dalacin C) | IV | 600 mgâ1.2 g/day (more severe: 1.2â2.7 g/day) | In 2â4 equal doses | SmPC: serious 600 mgâ1.2 g/day; more severe 1.2â2.7 g/day in 2â4 equal doses. High C. difficile risk. |
| UTI-focused agents | ||||
| Nitrofurantoin (Macrobid) | PO | 100 mg MR | BD with food | SmPC: 100 mg twice daily for uncomplicated lower UTI. Contraindicated if eGFR <45 mL/min. Not for pyelo/bacteraemia. |
| Nitrofurantoin (Macrodantin) | PO | 50 mg (100 mg if severe chronic recurrence) | QDS with food | SmPC: acute uncomplicated UTI 50 mg QDS; severe chronic recurrence 100 mg QDS. Same eGFR limits as Macrobid. |
| Trimethoprim (Monotrim) | PO | 200 mg | BD | Usual adult dose. Hyperkalaemia / folate antagonism; caution in renal impairment and with ACE/ARB/spironolactone. |
| Co-trimoxazole (Septrin Forte) | PO | 960 mg (160/800) | BD | Usual adult dose for many licensed infections. Sulphonamide allergy, hyperkalaemia, blood dyscrasias. |
| Co-trimoxazole (Septrin IV) | IV | 960 mg equivalent | BD | Standard adult infections often match oral 960 mg BD. PCP and other specialist indications are weight-based: use SmPC. |
| Aminoglycosides, glycopeptides, carbapenems & oxazolidinones | ||||
| Gentamicin (Genticin) | IV | Per SmPC / local AMS (often 3â5 mg/kg/day divided, or hospital extended-interval nomogram) | Per protocol | SmPC and Irish hospital practice differ: many sites use extended-interval regimens. Oto- / nephrotoxicity. Levels essential. |
| Vancomycin (Vancocin) | IV | 500 mg every 6 h or 1 g every 12 h | As SmPC / local AUC protocol | SmPC usual adult regimens above; many hospitals use weight-based dosing with levels. Infuse slowly (red-man syndrome). |
| Vancomycin (Vancocin) | PO | 125 mg | QDS | SmPC dose for C. difficile (not systemic infection). Severe CDI may use higher oral doses per SmPC / protocol. |
| Linezolid (Zyvox) | PO | 600 mg | BD | SmPC usual adult dose. MAO-I / serotonergic interactions; myelosuppression with longer courses. |
| Linezolid (Zyvox) | IV | 600 mg | BD | Same as PO. Near-complete oral bioavailability: switch to PO when absorbing. |
| Meropenem (Meronem) | IV | 500 mg or 1 g (2 g if meningitis / CF) | Every 8 h | SmPC adult table: most indications 500 mg or 1 g every 8 h; meningitis and CF 2 g every 8 h; FN usually 1 g every 8 h. |
Penicillins
Amoxicillin (Amoxil)
POSmPC is indication-based. Severe sinusitis/otitis may use 750 mgâ1 g every 8 h. GI upset; C. difficile risk.
Amoxicillin
IVUse the IV product SmPC. Higher doses exist for severe infection. Confirm local stock / AMS.
Co-amoxiclav (Augmentin)
POSmPC usual adult dose: one 500/125 mg three times a day. Take with food. Cholestatic jaundice risk with prolonged courses.
Co-amoxiclav (Augmentin)
POSmPC: BD for all indications; TDS for higher-dose needs (e.g. otitis, sinusitis, LRTI, UTI). Take with food.
Co-amoxiclav (Augmentin)
IVUsual adult IV SmPC dose. Review daily and switch to PO when suitable.
Flucloxacillin (Floxapen)
POIrish Floxapen SmPC: usual total 1â3 g/day in 3â4 divided doses (often 250â500 mg QDS). Empty stomach. Hepatotoxicity risk.
Flucloxacillin (Floxapen)
IVUsual IV SmPC range 250 mgâ1 g QDS; may be doubled in severe infection. Osteomyelitis/endocarditis: higher totals per product SmPC / AMS.
Phenoxymethylpenicillin (Pen V)
POEmpty stomach preferred. Not for serious systemic infection.
Benzylpenicillin (Crystapen)
IV / IMSmPC usual adult range; q4â6 h and higher totals for severe infection per product SmPC. Sodium load.
Piperacillin-tazobactam (Tazocin)
IVSee dedicated Tazocin topic / SmPC. No reliable oral switch. Pseudomonas cover.
Cephalosporins
Cefuroxime (Zinnat)
POAfter food. Not a like-for-like oral switch from IV cefuroxime.
Cefuroxime (Zinacef / Flynn)
IVSmPC usual 750 mg TDS; 1.5 g TDS for more serious infections. Confirm local AMS.
Ceftriaxone (Rocephin)
IV / IMSmPC usual adult range. Do not mix with calcium-containing infusions. Meningitis: higher dose per SmPC / protocol.
Cefalexin (Keflex)
POSmPC: most infections 500 mg every 8 h; SSTI/pharyngitis/mild UTI often 250 mg every 6 h or 500 mg every 12 h. Usual total 1â4 g/day.
Macrolides & tetracyclines
Clarithromycin (Klacid)
POSmPC: usual 250 mg BD; increase to 500 mg BD in severe infection. CYP3A4 interactions; QT prolongation.
Clarithromycin (Klacid IV)
IVSame interaction / QT cautions as PO. Switch to PO when absorbing.
Azithromycin (Zithromax)
POSmPC respiratory regimen commonly 500 mg once daily for 3 days (or day-1 500 mg then 250 mg for 4 days: check SmPC indication). QT risk.
Doxycycline (Vibramycin)
POSmPC usual: 200 mg on day 1, then 100 mg daily; 100 mg BD may be used. Avoid in pregnancy / children <12. Take upright with fluid.
Quinolones, metronidazole & clindamycin
Ciprofloxacin (Ciproxin)
POSmPC dose is indication-based within this range. Tendinopathy, CNS effects, QT, C. difficile. Separate from dairy/antacids.
Ciprofloxacin
IVSmPC usual 400 mg every 12 h; every 8 h for severe infection. Switch to PO when absorbing.
Metronidazole (Flagyl)
POIrish Flagyl SmPC for established anaerobic infection: 800 mg then 400 mg every 8 h. Other indications differ (e.g. BV 400 mg BD). Avoid alcohol.
Metronidazole (Flagyl)
IVUsual adult IV anaerobic dose. Switch to PO early when possible. Avoid alcohol.
Clindamycin (Dalacin C)
POSmPC: moderately severe 150â300 mg every 6 h; severe 300â450 mg every 6 h. High C. difficile risk.
Clindamycin (Dalacin C)
IVSmPC: serious 600 mgâ1.2 g/day; more severe 1.2â2.7 g/day in 2â4 equal doses. High C. difficile risk.
UTI-focused agents
Nitrofurantoin (Macrobid)
POSmPC: 100 mg twice daily for uncomplicated lower UTI. Contraindicated if eGFR <45 mL/min. Not for pyelo/bacteraemia.
Nitrofurantoin (Macrodantin)
POSmPC: acute uncomplicated UTI 50 mg QDS; severe chronic recurrence 100 mg QDS. Same eGFR limits as Macrobid.
Trimethoprim (Monotrim)
POUsual adult dose. Hyperkalaemia / folate antagonism; caution in renal impairment and with ACE/ARB/spironolactone.
Co-trimoxazole (Septrin Forte)
POUsual adult dose for many licensed infections. Sulphonamide allergy, hyperkalaemia, blood dyscrasias.
Co-trimoxazole (Septrin IV)
IVStandard adult infections often match oral 960 mg BD. PCP and other specialist indications are weight-based: use SmPC.
Aminoglycosides, glycopeptides, carbapenems & oxazolidinones
Gentamicin (Genticin)
IVSmPC and Irish hospital practice differ: many sites use extended-interval regimens. Oto- / nephrotoxicity. Levels essential.
Vancomycin (Vancocin)
IVSmPC usual adult regimens above; many hospitals use weight-based dosing with levels. Infuse slowly (red-man syndrome).
Vancomycin (Vancocin)
POSmPC dose for C. difficile (not systemic infection). Severe CDI may use higher oral doses per SmPC / protocol.
Linezolid (Zyvox)
POSmPC usual adult dose. MAO-I / serotonergic interactions; myelosuppression with longer courses.
Linezolid (Zyvox)
IVSame as PO. Near-complete oral bioavailability: switch to PO when absorbing.
Meropenem (Meronem)
IVSmPC adult table: most indications 500 mg or 1 g every 8 h; meningitis and CF 2 g every 8 h; FN usually 1 g every 8 h.
SmPCs (medicines.ie / HPRA)
â ïž Educational note
- This topic is for educational purposes only. It is not a substitute for local hospital antimicrobial guidelines, pharmacy advice, microbiology/AMS input, or the current Irish SmPC.
- Use the search bar above to find a drug or Irish brand name. Doses shown are usual adult SmPC regimens for normal renal and hepatic function.
- Always check allergy status (including β-lactam cross-reactivity), culture results, and whether a narrower agent or IV-to-oral switch is appropriate.
ð¡ How to use
- Irish brand names are shown in brackets where commonly used (e.g. Augmentin, Tazocin, Klacid, Flagyl, Macrobid). Generics are widely stocked; chart the generic name unless your hospital formulary prefers a brand.
- Where an antibiotic has more than one licensed route, each route is listed separately with its usual adult SmPC dose.
- For indication-specific pathways see CAP, cellulitis, febrile neutropenia, and related topics. For IV-to-oral switch see antibiotic IV-to-PO.
â ïž Safety & stewardship
- Start smart, then focus: take appropriate cultures before antibiotics when safe to do so, review at 48â72 h, and de-escalate or stop.
- Choose the narrowest effective agent and shortest evidence-based duration from local / HSE AMRIC guidance.
- Quinolones, clindamycin, and broad β-lactams carry higher C. difficile risk: counsel and review bowel habit.
- Adjust for renal impairment early (eGFR/CrCl). Aminoglycosides, vancomycin, nitrofurantoin, and many β-lactams need dose or agent changes.
- Document indication, dose, route, duration, and review date on the drug chart / ePMA.
- Pregnancy, lactation, extremes of weight, and significant drug interactions: check SmPC / pharmacy before charting.
ð SmPCs (medicines.ie)
- Open the current Irish SmPC before prescribing. Brands and generics change; medicines.ie / HPRA remain the source of truth.
- Linked SmPCs below cover many of the agents in the table. For products without a direct link (e.g. some amoxicillin, flucloxacillin, metronidazole, or IV-only lines), search medicines.ie or HPRA by INN / brand.
- Gentamicin and vancomycin: follow the product SmPC and your hospital TDM / AMS protocol. Indication-specific regimens can differ from the usual adult doses shown above.
Educational reference only. Medical disclaimer